Harvest control rules (HCRs) are the operational heartbeat of harvest strategies, laid down to stipulate how much fishing can take place on a certain resource based on indicators of its status. Recommended under the precautionary approach to fisheries management, HCRs derive management measures (for example quotas) necessary for attaining targets and avoiding limits in the context of prevailing uncertainty.
Given this inherent uncertainty in the system, weighing up how effective an HCR has been in achieving what it set out to achieve is important. For this reason, management strategy evaluations (MSEs) are used to assess the impact of the primary sources of the uncertainty. MSEs are therefore an important part of the process, giving insight into various fisheries resources and the fishing objectives set.
HCRs will constitute part of the Management Strategy Evaluation: an introduction course being held 28 August - 1 September at the ICES Secretariat in Copenhagen. Students will be guided through several case studies from around the world in which the harvest rules are analysed.
One such example is evident in a study conducted by José De Oliveira of CEFAS, who will run the tutorial alongside Carryn de Moor of the Marine Resource Assessment and Management (MARAM) at the University of Cape Town. De Oliveira took part in a management strategy evaluation of a total of 26 HCRs (divided into two basic types) that could potentially be used for western horse mackerel. Here, the performances of the two candidate HCRs were contrasted against each other and against the current HCR already in place. As is always useful in simulations of this sort, a no fishing scenario was also run to look at the dynamics of the stock if left unfished.
Using an underlying model based on the most recent ICES assessment of western horse mackerel, the evaluation set out to project horse mackerel populations under each rule, answering key questions including that of whether any of the rules could be considered precautionary in the short or longer term. In the mackerel's case, the existent HCR couldn't be: there was found to be a higher than 5% probability that the spawning stock biomass would fall below the reference point limit (Blim). To avoid this possibility of stock collapse, this HCR would require the activation of a further protection rule.
The candidate HCRs put forward for adoption were categorized as either 'Egg HCRs' or 'spawning stock biomass (SSB) HCRs', based on levels of horse mackerel egg data and SSB respectively. At a certain threshold, the Egg HCRs proved best in terms of minimizing risk and maximizing average catch. More generally, the egg HCRs outperformed the SSB ones.
Examples similar to the western horse mackerel one will be used alongside theoretical lectures during the tutorial. In addition to delving into the details of such example applications of MSE to test alternative HRCs, the course will include a number of other examples of MSEs used worldwide to enhance the course's theoretical lectures.